Process for the anti-static finishing of high molecular weight compounds



United States Patent 3,10,763' PROCESS FOR THE ANTI-STATIC FINISHING OF HIGH MOLECULAR WEIGHT COMPOUNDS Dietrich Schleede, Frankfurt am Main, Felix Schiilde, Neuenhain, Taunus, and Fritz Rochlitz, Frankfurt am Main, Germany, assignors to Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius & Briining, Frankfurt am Main, Germany, a corporation of Germany j No. Drawing. Filed Dec. 11, 1961, Ser. No. 158,585 Claims priority, application Germany, Dec. 17, 1960, F 32,784 6 Claims. (Cl. 106-186) I The present invention relates to a process for the antistatic finishing of high molecular weight compounds.

Shaped articles of any kind of high molecular weight materials, for example synthetic plastics, have a tendency towards electrostatic charging particularly when the material used possesses very good electric properties. Owingto this electrostatic charging these shaped articles, when used in practice, already exhibit dust deposits at the surface after a short time which deposits, in the case of .a strong electrostatic charging, show the wellknown zigzag design or crows feet. Owing to this strong electrostatic charging, moreover, sparking may occur on account of the great potential difference.

In the case of fibers or fabric-s the static charge manifests itself by rapid and strong dirtying of said fibers or fabrics. Owing to these disadvantages of the static charge, the use of such polymers may become uninterestingQ Many processes are known according to which electrostatic charging can be prevented or at least diminished. Thus it has been known for a long time, for example, to condition shaped articles after their fabrication, i.e. to expose them to moist air. Injection-molded pieces or fibers, for example of polyamide, cellulose acetate or viscose that are to be finished with an anti-static agent, absorb water to a certain extent .by this treatment whereby the electric conductivity is strongly increased.

Apart from the fact that some plastics, for example polyolefins, practically absorb no water and the shaped articles of this material cannot be finished with an antistatic agent in such a manner, this method also has the disadvantage that water content of the plastic articles is reversible, i.e. the anti-static effect is lost when storing the articles treated in this manner in a dry atmosphere.

Since it is in most cases not sufiicient to expose the shaped articles to moist air in order to obtain an antistatic ettect,.various processes have been developed in which the plastics material or the surface of the shaped articles made therefrom is modified by means of antistatic agents in such a manner that the static charge is diminished. Quite a number of compounds have been proposed for this purpose. These compounds can be classified in the following five groups:

(1) Nitrogen-containing compounds such as amines, amides, and quaternary ammonium salts,

(2) Sultonic acids and aryl-alkyl-sulfonates,

(3) Phosphoric acids and aryl-alkyl phosphates, as well as phosphoric acid ester amides,

(4) Polygly-cols and the derivatives thereof including polyglycol estersof fatty acids as well as polyglycol aryl alkyl ethers,

(5) Polymers of multivalent alcohols and the derivatives thereof. 1 i y The anti-static agents can be applied to the shaped articles made of plastics materials by treating them with a solution of said agents. They may, however, also be incorporated by admixing the respective agents to the plastics powder prior to its processing.

3,199,763 Patented June 22, 1965 case of the anti-static agents known hither-to so that they are effective during a limited period only on account of abrasion and when being used everyday. Moreover, the danger exists that the surface of the material is changed. Some of the anti-static agents to be applied are exceedingly hygroscopic so that they abs-orb an un necessarily large amount of water. They are, moreover, in most cases not harmless from a physiological point of view.

An anti-static treatment by incorporating the anti-static agents has the advantage that it is possible at any time to finish high molecular weight materials on demand with anti-static agents also after their polymerization;

In order to attain a suificient anti-static effect the al-. ready known organic compounds that arecapable of being incorporated 'must, however, be added in amounts which entail a modification of the characteristic properties of the plastics material such, for example, as a decrease of the temperature ranges suitable for the processing, a reduction of the hardness, the rigidity, the thermostability under load, a deterioration of the color, etc'. In many cases the compounds concerned are agents by whose incorporation the high molecular weight material finished therewith loses its physiological harmlessness.

Reallyeifective anti-static agents that can be applied on an industrial scale for the incorporation in synthetic plastics are not known hither-to.

Another possibilty of rendering high molecular weight materials resistant to electrostatic charge consists in incorporating additives during the polymerization. This method has the disadvantages that the high molecular weight material is rendered resistant to electrostatic charge already in the manufacturing process, while the fabricator can in many cases decide only shortly before the final shaping whether an anti-static finishing is required for the desired purpose, or whether the slight deterioration of the electrical properties connected therewith is unwelcome. Moreover, by adding the hitherto known additives during the polymerization the characteristic properties of the materials, for example the absorption of water, the chemical resistance, toughness, and hardness are modified in many cases.

Now we have found that organic compounds of high molecular weight can be finished with the aid of antistatic agents by the incorporation of substituted ureas or thio-ureas of the general formula Y wherein X represents :0 or =8, Y represents -N(R in which the two radicals need not be equal, or N:R R represents alkyl (containing 1 to 20 carbon atoms), prefer-ably -methyl, R represents -H, -alkyl (containing 1 to 20 carbon atoms), -cycloalkyl, -aryl, or alkylaryl, R represents :alkyl (containing 1 to 20 carbon atoms), :cycloalkyl or =alkylaryl.

The hydrocarbon radicals may also be substituted, for example by halogens, amino groups, substituted amino groups, oxy groups, alk-oxy groups, thio ether, mercaptane groups, sulfonamide groups, carboxy alkyl groups, for ex ample the carboxylauryl groups, carboxycetal groups, etc., aryl groups or alkylaryl groups.

Compounds containing several substituted u-reaor thi-o urea groups in the molecule, for example connected one with the other by an alkyl radical, also have good antistatic properties.

The compounds described may be added to the plastics materials both as such and also as ammonium salts together with inorganic or, preferably, organic acids.

It is advantageous to admix the anti-static agents to the plastics materials in a concentration of 0.1 to 7 percent by weight, preferably 0.5 to 4 percent by weight. Ureas or thio ureas, in which R and R represent aliphatic radicals or H, generally have the best anti-static effect, above all in the case when R represents a methyl group and at least one of the radicals R rep-resents a longer alkyl radical such, for example, as the stearylor dodecyl radical.

As suitable anti-static agents there may be used, for example, the following compounds without limiting the process to these compounds:

N,N dimethyl urea, N,N methylstearyl urea, ltetraethyl urea, N,N didodccyl urea, N,N methylstearyl thio urea, triacetone diurea, hexymethylene- 1,6 bis (w butylthio urea), phenyl thio urea, N,N-bis-(3-aminophenyl)-urea, etc. The use of urea and thio-urea for the subsequent anti-static finishing of finished fibers and filaments by spraying a solution or an aqueous dispersion on to the fibers and filaments has already been described. These unsubstituted ureas are not suited, however, for incorporation in plastics materials since their efficacy is lost when being processed. Owing to the high temperatures there probably sets in decomposition of the compounds in the course of the thermoplastic shaping process. That this is probably the case is also indicated by the strong discoloration manifesting itself during the processing.

In a proposal not .belonging to the state of the art it has been suggested that phosphoric acid-Nmethylstearylamide-diamide be used as an anti-static agent. Although this compound is an extremely effective agent it cannot be used in all fields of application with the same good success. Thus, for example, phosphoric-acid N-methylstearylamide-diamide is water-soluble to a certain extent so that it is'less suited for the anti-static finishing of fabrics or shaped articles which, after :being processed, are often subjected to a Washing process.

It is a special advantage of the present invention that quite a category of compounds are described as antistatic agents so that of the great number of effective products there may, according to requirements, be chosen compounds particularly suited for a certain synthetic plasticor for a special field of application. According to the special requirements of the services there may be chosen compounds which, on account of their solubility in water or organic solvents or in the synthetic plastic itself, or owing to their color, decomposition, meltingor boiling temperature, etc., yield final products having optimum properties. In many cases it may also be advantageous to use mixtures of two or several of the compounds described.

An anti-static effect is attained already when adding small amounts of the said compounds to the synthetic plastics so that shaped articles made from such mixtures no longer charge electrostatically at the surface and no longer have a tendency to attract dust. The mechanical and thermal properties, the thermostability under load as well as color and transparency of the polymers are practically not altered by the addition of the said compounds.

The working conditions and the temperature range in which the synthetic plastics can be shaped by a thermoplastic process remain the same. Moreover, the products are Well compatible with all polymers. The anti static effect that can be attained is independenet of the moisture of the surroundings and practically of an unlimited duration. Exudation was not observed. Moreover, the surface does not become hydroscopic but remains unchanged. The electric properties of the polymers are, of course, influenced by the addition of antistatic agents for this constitutes their anti-static efiicacy. The deterioration of the specific transmissionand surface resistivity as well as of the dielectric properties is so trifling, however, that in most cases it is of no consequence even for the application of the polymers in the field of electrical engineering.

By adding compounds of the category as described above all high molecular weight materials can be improved that have the tendency of getting dirty by attracting dust owing to electrostatic charging. These compounds exhibit a particularly good efficacy, for example, in polystyrene and in the copolymers of styrene with butadiene, acrylonitrile and/or vinyl carbazole, in polyvinyl chloride and vinyl chloride copolymers, polyterephthalates, polyolefins obtained by the high pressure or low pressure process (Phillips, Ziegler process), such as the polymers and copolymers of ethylene, propylene, butene (1), pentene (1), 4 methyl pentene (1), hexene (1), 5,5 dimethyl hexene (1), octadecene (1), 4 phenylbutene (1) as well as vinylcyolohexene, poly-carbonates, polyformaldehydes, polyacrylonitrile, polyacrylic acid esters, polymethacrylic acid esters, polyamides, polyurethanes, polyvinyl esters, polyacetals, polymers of fiuor-olefins, cellulose derivatives and polymer mixtures containing the aforementioned polymers. Also unsaturated polyesters and epoxide resins hardened with reagents having a basic character as well as raw materials for lacquers can without difficulties acquire an anti-static finishing prior to or during their processing by an addition of the compounds cited.

The substituted ureas or thio-ureas can be added prior to or during the polymerization, and also later on to the pulverulent high molecular weight polymer as well as to the granular product. Depending on the nature of the synthetic plastic the ureas can be admixed in the melt, in solution and by application to the pulverulent or granular high molecular weight polymer. The admixture is most advantageously effected prior to or during the processing. It was found that the technique of incorporation is of little importance. It is important, however, that the anti-static agents are distributed in the synthetic plastic as evenly as possible.

The high molecular weight polymers provided with an anti-static finishing can be processed by all customary processing methods, for example on molding presses, injection molding machines or extruders. From these high molecular weight polymer-s, therefore, there can be made compressionand injection-molded articles, semifinished goods, sheets, inflated hollow articles, tubes, fibers, filaments, monofilaments, etc. The resin admixed with the compounds mentioned above can be processed in the usual manner as resin varnish or casting resin or in combination with glass fibers and/or fillers.

The high molecular weight polymers finished in this manner are especially interesting for packaging purposes (packing-material, canisters, bottles, beakers), as accessories for vacuum cleaners, band-conveyors, showroom patterns, and masters, parts for casings (for example for radioand television sets, vacuum cleaners), electric installations such as lighting fixtures, cable insulations, plugs, switches or armatures, air conditioning and ventilating equipments, plastics table ware, kitchen machinery, filaments, fibers, fabrics, sheets, lacquers, that is to say in all those cases in which an anti-static finishing is required.

The anti-static effect of inorganic or organic compounds in high molecular weight materials can be determined most easily by means of cigarette ash. For testing these materials plates obtained by extrusion, injectionor compression-molding are vigorously rubbed with a.- woollenclothfor .about .15 secondsandheld. about 2 mm. above a layer of cigarette ash. When the extruded or molded plates have good anti-static properties, they do 6 homogenizing, the material was worked up into granules which were. processed.intominjection-molded plates.

Examples 2, 4, 5, and 6 not attract cigarette ash. v The indicated amounts of the anti-static agents were Another method for determining the electrostatic applied i the form fa powder t 10 kilos of the indicharge consists in measuring the specific transinlsslon cated granular plastic material according to the dry dyeresistivity. An attraction Of cigarette ash was no longer ing process, A'roller vat was used as a means for applyobserved when the transmission resistivity had a value ing the anti-staticagent. The material thus treated was of about $10 ohms/centimeter. 10 extruded; worked up into granules and injection-molded When measuring the transmission resistivity it cannot into 1mm. thick plates. in each case be determined exactly whether an anti-static, effect has been attained or not. In many cases the anti Example 3 Static efiicacy is brought abollt y a reduction of the In a mixer 10 kilos of isotactic polypropylene were values for: the surface resistivity. In those cases the 15 ixed.with 1,000 grams of a. hot 10% solution of transmission resistivity y be g an attraction of ash, hexamethylene-1,6-bis-w-butyl-thio-urea in acetone. Afnevef'fheless, be non-eXlsient ter evaporating the solvent at 75 C. the product was Qlllt6 a number of fuftherfmethods are known for worked up into granules which were injection-molded determining the electrostatic charge, but itwas found i plates that only the two testing methods mentioned above fur- 0 Example 7 nish genuine values which approach those found in practice 200 grams of :a commercial unsaturated polyester resin Table 1 which lists the test results shows that an excelg i i %"i 2 2 i i i fi lent anti-static effect can be attained with all of the mo 0 ma em a y n I an mo o p ale V a V anhydndeand subsequentdissolutlon of the condensacompounds enumerated. d 307 b ht f t t The following examples serve to illustrate the inven- 2 g z fi s f i' 0 tion but they are not intended to-lir'nit it thereto, the parts p a a 6 a 1 10110 0 0 me y e y 6 one peroxide, 0.1% of cobaltous naphthenate as well as 1% being by weight.

EXAMPLES of N,NdnfithYlStCflIYl-thlO-llffifi and hardened at room u temperature with the exclusion of air.

Several ans-Static compounds corresponding to the The examplesdescribedrepresent, of course, only a $l1mmai10nif?rmi11i}' explfllned' I the deS CfiPt10n were small'selectionof the existing possibilities. The anti- P Q hlgh liloleculal Welght p y static effect attainable is not restricted to the aforemen- Theiantl-stflilc agents P' amounts 'added'thereofi tioned compounds or to the combinations with plastics 3ndthe-te$ tre$1 11t$alellsted 111 Table I materials as described in Table 1; As anti-static agents The anti-Smile agents Incorporated 111 the follow there may be used with the same success also other comlng manner: pounds corresponding to the summation formula in the Example 1 description. In a combination with plastics materials In a mixer 100 grams f molten NsNzdimethypurea care has only to be taken that the decomposition point were introduced'through nozzles into -10 kilos of linear f tilt? compounds used as anti-Static agents is not IOWel' (low pressure) polyethylene powder. After thorough than the working temperature of the plastics material.

TABLE 1 Transmission Transmission 1 resistivity resistivity Ex. No. Plasticsmaterial used of the Anti-staticagent Structural formula of the Addition, Attraction after the plastics. Anti-static agent percent of ash addition, material, ohms. cm. ohms. cm.

7 IIIH-CHa 1 Linear (low-pressure) 101B N,N dimethylurea. O=O V 1 10 polyethylene. l NH-CHa CISHB'I" NCH3 2 Po1ystyrene 10 N,N-n1ethylstearylurea 0=(]J 1 10 2 3 3 Polypropylene l0 Hexamethylene-l,6-bis- CHz-NHC-NHC4H0 1 10 8 w-butyl-thiourea. r

onz mzu -nn-oint i, 4 Butadiene/styrene 10" do OHz-NHCNHC4H9 1 10 eopolymer.

(CHM

CHz-NH-?[JNHC4HQ TABLE 1 Transmission Transmission resistivity resistivity EX.N0. Plastics material used of the Anti-static agent Structural formula of the Addition, Attraction after the plastics Anti-static agent percent of ash addition, material, ohms. cm. ohms. cm.

i I?C1aHa1 5 Acrylonitrile/styrene 7 10 Methylstcarylurea O=C 0.75 10 copolymer. I

N NIT-Cat n 6 Branched (high-pres- 10 N,N-distcarylurca 0:0 1 10 sure) polyethylene. l

N -(318 31 1 -C1s s1 7 Polyester casting or 10 Methylstearylthio-urca S=C lacquer coat.

We claim: 1. A composition of matter consisting essentially of N (a) a synthetic plastic of high molecular weight selected from the group consisting of polystyrene, a copolymer =0 of styrene with butadiene, a copolymer of styrene with acrylonitrile, a copolymer of styrene with vinyl carbazole, N polyvinyl chloride, 2. polyterephthalate, a polyolefin, a

polycarbonate, polyacrylonitrile, a polyacrylic acid ester, a polymethacrylic acid ester, a polyamide, a polyurethane, a polyvinyl ester, a polyacetal, a polymer of a fluoroolcfin, a cellulosic polymer, an unsaturated polyester, and an epoxy resin, said plastic having incorporated therein and distributed therethrough, (b) 0.l-7% by weight, based on the plastic, of a compound of the formula:

wherein X is a radical selected from the group consisting of oxygen and sulfur, R is a radical selected from the group consisting of H and CH R is an alkyl polymer which has a tendency to get dirty by attracting dust owing to electrostatic charging, which process consists essentially of incorporating an anti-static agent into said plastic in the course of its processing and distributing it substantially uniformly therethrough, said antistatic agent being present in said plastic in an amount of 0.1-7% by weight, based on the weight of the plastic, and having a chemical structure of the formula:

group containing 1-20 carbon atoms, and R and R are r wherein X is a radical selected from the group consisting of oxygen and sulfur, R is a radical selected from the group consisting of -H and CH R is an alkyl group containing 1 20 carbon atoms, and R and R are each selected from the group consisting of H, phenyl, and alkyl, the alkyl groups containing 1-20 carbon atoms each, and R and R may be substituted by a radical selected from the group consisting of an amino group, a hydroxy group, and a carbonyl group.

3. The process of claim 2 wherein said anti-static agent is incorporated into the plastic in the melt.

4. The process of claim 2 wherein said anti-static agent is incorporated into the plastic in powder form.

5. The process of claim 2 wherein said anti-static agent is incorporated into the plastic by mixing both components in solution form.

6. The process of claim 2 wherein said high molecular weight polymer isselected from the group consisting of polystyrene, a copolymer of styrene with butadiene, a copolymer of styrene with acrylonitrile, a copolymer of styrene with vinyl carbazole, polyvinyl chloride, a polyterephthalate, a polyolefin, a polycarbonate, polyacrylonitrile, a polyacrylic acid ester, a polymethacrylic acid ester, a polyamide, a polyurethane, a polyvinyl ester, a polyacetal, a polymer of a fluoroolefin, a cellulosic polymer, an unsaturated polyester, and an epoxy resin.

References Cited in the file of this patent UNITED STATES PATENTS 2,050,582 Orthner et a1 Aug. 11, 1936 2,165,265- Hubert et a1 July 11, 1939 2,657,984 Braithwaite et a1 Nov. 3, 1953 2,730,464 Winsor Jan. 10, 1956 FOREIGN PATENTS 521,958 Canada Feb. 21, 1956 

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF (A) A SYNTHETIC PLASTIC OF HIGH MOLECULAR WEIGHT SELECTED FROM THE GROUP CONSISTING OF POLYSTYRENE, A COPOLYMER OF STYRENE WITH BUTADIENE, A COPOLYMER OF STYRENE WITH ACRYLONITRILE, A COPOLYMER OF STYRENE WITH VINYL CARBAZOLE, POLYVINYL CHLORIDE, A POLYTEREPHTHALATE, A POLYOLEFIN, A POLYCARBONATE, POLYACRYLONITRILE, A POLYACRYLIC ACID ESTER, A POLYMETHACRYLIC ACID ESTER, A POLYAMIDE, A POLYURETHANE, A POLYVINYL ESTER, A POLYACETAL, A POLYMER OF A FLUOROOLEFIN, A CELLULOSIC POLYMER, AND UNSATURATED POLYESTER, AND AN EPOXY RESIN, SAID PLASTIC HAVING INCORPORATED THEREIN AND DISTRIBUTED THERETHROUGH, (B) 0.1-7% BY WEIGHT, BASED ON THE PLASTIC, OF A COMPOUND OF THE FORMULA: 